When performing an online waterwash, our 6B changed from Premix Steady State to Lean-lean negative. We backed the generator down to lean-lean positive and started loading the turbine. It changed back to Premix and then we base-loaded it. We run in baseload all the time. This is the second time this has happened. Both times were when we were waterwashing.

 

RedJim,

A few questions. First, how long have you been doing on-line water-washes on your Frame 6B? (I presume for a period of several years; but please be as specific as possible.)

Second, how long has the unit had the DLN-I+ combustion system? (In other words, was it a DLN-I unit before being upgraded to DLN-I+, or did it have conventional combustors, and then was "recently" upgraded to DLN-I+?)

Third, have you switched detergents or detergent manufacturers recently?

Fourth, is the detergent you've used when you experienced the problems you are describing detergent water-based or oil/solvent-based?

Fifth, what does GE say about the problem?

The only time I've seen off-line water washing cause a problem for a DLN-I machine (and it was a Frame 6B transfer-less DLN-I unit) is when solvent-based detergent was used. The solvent ignited in the primary combustion zone and when the Speedtronic saw flame in the primary combustion zone it automatically went to Extended Lean-Lean (sometimes also called Lean-Lean Negative on older DLN-I units). GE's recommendation was not to use a solvent-based detergent, but rather to use a water-based detergent. And, that solved the problem.

I've been told that some water-based detergents are more expensive than their solvent-based counterparts (I don't actually know if that's true or not).

I've also been told that water-based detergents generally aren't as effective as solvent-based detergents, but when one can't use solvent-based detergents without having to reduce load (or transfer to Extended Lean-Lean/Lean-Lean Negative to perform an on-line water wash when using a solvent-based detergent) there aren't many options short of shutting down to perform an off-line water wash. Most sites with DLN-I units perform on-line water washes with water-based detergents, and perform off-line water washes with solvent-based detergents for the best results.

That's about as much as I can offer as I'm only vaguely familiar with the DLN-I+ combustion system hardware and controls. Hope this helps.

 

Here's some answers.

1. We wash daily, as long as the temp is above 50 degrees. We alternate, One day demin water, the next day we use a non-solvent base soap.

2. We were the alpha unit for DLN1+ conversion. Unit was built in 1985,conventional combusters, non DLN, Mark 4. We upgraded to DLN1+ in 2008 with Mark 6.

3. Non-solvent base soap.

4. We have been using this wash cycle, system, and soap for 20 years. 5. Still waiting on comments from GE.

We've used non-solvent soap for both online and offline crankwash cleanings. The compressor is clean when we come down for HGP and CI's. I think that if you have an oil leak on the #1 bearing, then you may have issues using soap.

Thanks,
Jim

 

Jim,

when the unit drops out of Premix into Lean Lean are there any other alarms that annunciate?

I know when we used to perform online washed we would watch the flame scanner counts and actually stop the wash if counts started to decrease on more than one scanner. This usually signaled fogging of the scanners. But as you know I'm sure, the concern here was tripping the unit on loss of flame, not dropping out of premix. I'm just trying to understand the reason for the drop out of premix. Is the MKVI seeing flame in the primary and relighting the unit into extended lean lean, or is something happening with the TTRF temperature making the unit think it needs to transfer?